Tractor heritage, news and features

International rescue

Where do you start with this tractor? Selectable four-wheel drive, selectable four-wheel steering, six-cylinder turbo engine, 150 horsepower. These statistics are impressive enough even when applied to a modern machine. Now consider that this tractor’s predecessor, the International Harvester 4166, was introduced in 1972; and even this, the 4186, the next model to be introduced, came out in 1977, over three decades ago.

Big power and torque figures are useless unless they can be put to use; naturally four-wheel drive helps, but even with this, without some clever work on the weight distribution, much of the advantage can be negated.

The design of the International takes this into account and the mass has been distributed so that at rest over 60 per cent of the tractor’s weight is on the front wheels. As the pull is taken up, this evens out as weight transfer lifts the front and shifts some of the load from the front wheels to the rears. The result is that under the conditions where maximum traction is needed, good use of the laws of physics means that it effectively has a 50/50 weight balance and equal traction from all four tyres.

Building a four-wheel drive tractor inevitably involves some compromises. Having all four wheels roughly the same size as the rear wheels on a two-wheel drive is somewhere near the ideal, as within reason the bigger the radius of the wheel/tyre combination, the better they are for comfort, grip and the ability to climb over obstacles. You only have to compare a bicycle wheel to a castor from a shopping trolley to realise that the bike wheel not only touches the ground over a greater area but can also roll over much larger obstacles with comparative ease.

But if you make the front wheels as large as the rears, you can’t turn the steering much before the tyres hit the chassis frame; the expensive solution was to redesign the machine totally and hinge the tractor in the middle like a Doe. But usually the compromise was to make the wheels smaller and if more grip was needed, the tyres wider.

Pathway

The International goes halfway down this particular pathway; all four of the wheels are slightly smaller than most rear wheels plus they are very wide. Although they are reduced in diameter, the additional width of the International\'s rims do present problems too; back to the tyres rubbing on the chassis when the wheels are turned...

The fix used by International wasn’t new but it did solve their problems, they figured that if you can only turn the steered wheels by half the amount, why not steer twice as many wheels? 

Four-wheel steering was the answer and was achieved by the use of two ‘front’-type axles, one at each end of the International, each equipped with a swivel hub assembly; the use of hydraulic rams making the choice between two- or four-wheel steering easy, a simple valve being used to isolate the rear ram when necessary.

The difference in turning circle between front-wheel steer and four-wheel steer is marked; using just the front wheels, the International will  turn a full circle in 295 inches, whereas using four-wheel steer, that figure is reduced to 187 inches – one heck of an improvement.

The cost to pay for this improvement is complicated; there is now twice as much to maintain as before, four swivels to keep an eye on, two sets of universal joints, extra steering rams, and the list goes on. As ever, I don’t want to get carried away with criticism of the design; it works and works well, although ironically the one thing that this tractor hasn’t done much is work!

Its history is that it was used from new exclusively in the construction industry rather than for agricultural work, so the 3300 hours recorded are very probably genuine. The complete lack of wear around the ball joints certainly backs up the construction work story; I doubt that the three-point linkage has ever been used in anger.

This is an American market-only tractor and is believed to be the only one here in the UK. The inside of the cab is pure 1970s US design and by UK standards of the time, it is the height of luxury – a spring seat, air conditioning, a powerful heater and radio (a wonderful period example too). There is even an amount of sound deadening to make the hours sat in the cab easier on the ears (the Nebraska Tractor tests recorded 89Dba). It isn’t the insulated padded cocoon that the modern operator takes for granted though; painted steel surfaces with levers sprouting out of them abound and there is nothing more sophisticated than rubber gaiters to keep muck and dust out of the cab.

Stern warning notices tell the driver that for transport, two-wheel steering and two-wheel drive must be used; another urges the driver to, REMEMBER: TRACTORS CAN BE ROLLED OVER. Serious stuff. Driver safety was at least taken seriously; you only need to look at the square section rollover cage with its double-gusseted corners to realise that the great weight of the 4186 would crush anything less – not a nice thought to dwell upon.

Good look

Stepping back and taking a good look at the International, my thoughts were that it very much has the look of a Muir Hill about it. Of course, this is entirely coincidental; any four-wheel drive tractors with a central cab will inevitably look much the same as others built at around the same period in time. The 4186 does however have an extra something about it; maybe it is the width of the cab and the bonnet which accentuate the short wheelbase, or perhaps it is the way it sits, four square on its ultra-wide tyres, or perhaps it is a combination of bits – suffice to say, it has a real air of purpose about it.

The purposeful look is backed up by the way it performs; I was lucky enough to have the International worked for me while coupled to a hefty set of modern discs that gave the tractor something to really get its teeth into.

It’s a shame that pictures can’t convey sound, for the noise of the 4186 working is as impressive as the way it looks. An inline six-cylinder engine, be it petrol or diesel, always sounds good when it is under load; and this one being silenced by nothing more than the turbocharger and a short length of big bore exhaust really has a fabulous sound.

Even at idle, it has a distinctive note, a rumble overlaid by the turbocharger whistle, strangely reminiscent of a diesel railway loco ticking over I thought.

When it is pulling hard, you get a real impression of the power and torque being produced. It is the start from rest that is the most impressive; there is a pall of smoke from the exhaust, an increase in volume of the turbo whistle and the engine really barks as the Inter starts to pull; then it’s all over and the big six settles down to a contented growl. While it was obvious that the discs were giving the 4186 something to get its teeth into, I’m pretty sure that it had much more to give.
You can expect to see the 4186 working at selected events during 2010, and then you can decide for yourself if I’m right.